--- a/layout/style/nsComputedDOMStyle.cpp
+++ b/layout/style/nsComputedDOMStyle.cpp
@@ -2172,16 +2172,42 @@ nsComputedDOMStyle::DoGetImageLayerPosit
     SetValueToPosition(aLayers.mLayers[i].mPosition, itemList);
     valueList->AppendCSSValue(itemList.forget());
   }
 
   return valueList.forget();
 }
 
 already_AddRefed<CSSValue>
+nsComputedDOMStyle::DoGetImageLayerPositionX(const nsStyleImageLayers& aLayers)
+{
+  RefPtr<nsDOMCSSValueList> valueList = GetROCSSValueList(true);
+  for (uint32_t i = 0, i_end = aLayers.mPositionXCount; i < i_end; ++i) {
+    RefPtr<nsROCSSPrimitiveValue> val = new nsROCSSPrimitiveValue;
+    SetValueToPositionCoord(aLayers.mLayers[i].mPosition.mXPosition, val);
+    valueList->AppendCSSValue(val.forget());
+  }
+
+  return valueList.forget();
+}
+
+already_AddRefed<CSSValue>
+nsComputedDOMStyle::DoGetImageLayerPositionY(const nsStyleImageLayers& aLayers)
+{
+  RefPtr<nsDOMCSSValueList> valueList = GetROCSSValueList(true);
+  for (uint32_t i = 0, i_end = aLayers.mPositionYCount; i < i_end; ++i) {
+    RefPtr<nsROCSSPrimitiveValue> val = new nsROCSSPrimitiveValue;
+    SetValueToPositionCoord(aLayers.mLayers[i].mPosition.mYPosition, val);
+    valueList->AppendCSSValue(val.forget());
+  }
+
+  return valueList.forget();
+}
+
+already_AddRefed<CSSValue>
 nsComputedDOMStyle::DoGetImageLayerRepeat(const nsStyleImageLayers& aLayers)
 {
   RefPtr<nsDOMCSSValueList> valueList = GetROCSSValueList(true);
 
   for (uint32_t i = 0, i_end = aLayers.mRepeatCount; i < i_end; ++i) {
     RefPtr<nsDOMCSSValueList> itemList = GetROCSSValueList(false);
     RefPtr<nsROCSSPrimitiveValue> valX = new nsROCSSPrimitiveValue;
 
@@ -2361,16 +2387,30 @@ nsComputedDOMStyle::SetValueToPosition(
 already_AddRefed<CSSValue>
 nsComputedDOMStyle::DoGetBackgroundPosition()
 {
   const nsStyleImageLayers& layers = StyleBackground()->mImage;
   return DoGetImageLayerPosition(layers);
 }
 
 already_AddRefed<CSSValue>
+nsComputedDOMStyle::DoGetBackgroundPositionX()
+{
+  const nsStyleImageLayers& layers = StyleBackground()->mImage;
+  return DoGetImageLayerPositionX(layers);
+}
+
+already_AddRefed<CSSValue>
+nsComputedDOMStyle::DoGetBackgroundPositionY()
+{
+  const nsStyleImageLayers& layers = StyleBackground()->mImage;
+  return DoGetImageLayerPositionY(layers);
+}
+
+already_AddRefed<CSSValue>
 nsComputedDOMStyle::DoGetBackgroundRepeat()
 {
   const nsStyleImageLayers& layers = StyleBackground()->mImage;
   return DoGetImageLayerRepeat(layers);
 }
 
 already_AddRefed<CSSValue>
 nsComputedDOMStyle::DoGetBackgroundSize()
@@ -6119,16 +6159,30 @@ nsComputedDOMStyle::DoGetMaskOrigin()
 already_AddRefed<CSSValue>
 nsComputedDOMStyle::DoGetMaskPosition()
 {
   const nsStyleImageLayers& layers = StyleSVGReset()->mMask;
   return DoGetImageLayerPosition(layers);
 }
 
 already_AddRefed<CSSValue>
+nsComputedDOMStyle::DoGetMaskPositionX()
+{
+  const nsStyleImageLayers& layers = StyleSVGReset()->mMask;
+  return DoGetImageLayerPositionX(layers);
+}
+
+already_AddRefed<CSSValue>
+nsComputedDOMStyle::DoGetMaskPositionY()
+{
+  const nsStyleImageLayers& layers = StyleSVGReset()->mMask;
+  return DoGetImageLayerPositionY(layers);
+}
+
+already_AddRefed<CSSValue>
 nsComputedDOMStyle::DoGetMaskRepeat()
 {
   const nsStyleImageLayers& layers = StyleSVGReset()->mMask;
   return DoGetImageLayerRepeat(layers);
 }
 
 already_AddRefed<CSSValue>
 nsComputedDOMStyle::DoGetMaskSize()

--- a/layout/style/nsComputedDOMStyle.h
+++ b/layout/style/nsComputedDOMStyle.h
@@ -283,35 +283,41 @@ private:
   already_AddRefed<CSSValue> DoGetGridRowStart();
   already_AddRefed<CSSValue> DoGetGridRowEnd();
   already_AddRefed<CSSValue> DoGetGridColumnGap();
   already_AddRefed<CSSValue> DoGetGridRowGap();
 
   /* StyleImageLayer properties */
   already_AddRefed<CSSValue> DoGetImageLayerImage(const nsStyleImageLayers& aLayers);
   already_AddRefed<CSSValue> DoGetImageLayerPosition(const nsStyleImageLayers& aLayers);
+  already_AddRefed<CSSValue> DoGetImageLayerPositionX(const nsStyleImageLayers& aLayers);
+  already_AddRefed<CSSValue> DoGetImageLayerPositionY(const nsStyleImageLayers& aLayers);
   already_AddRefed<CSSValue> DoGetImageLayerRepeat(const nsStyleImageLayers& aLayers);
   already_AddRefed<CSSValue> DoGetImageLayerSize(const nsStyleImageLayers& aLayers);
 
   /* Background properties */
   already_AddRefed<CSSValue> DoGetBackgroundAttachment();
   already_AddRefed<CSSValue> DoGetBackgroundColor();
   already_AddRefed<CSSValue> DoGetBackgroundImage();
   already_AddRefed<CSSValue> DoGetBackgroundPosition();
+  already_AddRefed<CSSValue> DoGetBackgroundPositionX();
+  already_AddRefed<CSSValue> DoGetBackgroundPositionY();
   already_AddRefed<CSSValue> DoGetBackgroundRepeat();
   already_AddRefed<CSSValue> DoGetBackgroundClip();
   already_AddRefed<CSSValue> DoGetBackgroundBlendMode();
   already_AddRefed<CSSValue> DoGetBackgroundOrigin();
   already_AddRefed<CSSValue> DoGetBackgroundSize();
 
   /* Mask properties */
   already_AddRefed<CSSValue> DoGetMask();
 #ifdef MOZ_ENABLE_MASK_AS_SHORTHAND
   already_AddRefed<CSSValue> DoGetMaskImage();
   already_AddRefed<CSSValue> DoGetMaskPosition();
+  already_AddRefed<CSSValue> DoGetMaskPositionX();
+  already_AddRefed<CSSValue> DoGetMaskPositionY();
   already_AddRefed<CSSValue> DoGetMaskRepeat();
   already_AddRefed<CSSValue> DoGetMaskClip();
   already_AddRefed<CSSValue> DoGetMaskOrigin();
   already_AddRefed<CSSValue> DoGetMaskSize();
   already_AddRefed<CSSValue> DoGetMaskMode();
   already_AddRefed<CSSValue> DoGetMaskComposite();
 #endif
   /* Padding properties */

--- a/layout/style/nsComputedDOMStylePropertyList.h
+++ b/layout/style/nsComputedDOMStylePropertyList.h
@@ -55,16 +55,18 @@ COMPUTED_STYLE_PROP(backface_visibility,
 //// COMPUTED_STYLE_PROP(background,               Background)
 COMPUTED_STYLE_PROP(background_attachment,         BackgroundAttachment)
 COMPUTED_STYLE_PROP(background_blend_mode,         BackgroundBlendMode)
 COMPUTED_STYLE_PROP(background_clip,               BackgroundClip)
 COMPUTED_STYLE_PROP(background_color,              BackgroundColor)
 COMPUTED_STYLE_PROP(background_image,              BackgroundImage)
 COMPUTED_STYLE_PROP(background_origin,             BackgroundOrigin)
 COMPUTED_STYLE_PROP(background_position,           BackgroundPosition)
+COMPUTED_STYLE_PROP(background_position_x,         BackgroundPositionX)
+COMPUTED_STYLE_PROP(background_position_y,         BackgroundPositionY)
 COMPUTED_STYLE_PROP(background_repeat,             BackgroundRepeat)
 COMPUTED_STYLE_PROP(background_size,               BackgroundSize)
 //// COMPUTED_STYLE_PROP(border,                   Border)
 //// COMPUTED_STYLE_PROP(border_bottom,            BorderBottom)
 COMPUTED_STYLE_PROP(border_bottom_color,           BorderBottomColor)
 COMPUTED_STYLE_PROP(border_bottom_left_radius,     BorderBottomLeftRadius)
 COMPUTED_STYLE_PROP(border_bottom_right_radius,    BorderBottomRightRadius)
 COMPUTED_STYLE_PROP(border_bottom_style,           BorderBottomStyle)
@@ -330,16 +332,18 @@ COMPUTED_STYLE_PROP(marker_start,       
 COMPUTED_STYLE_PROP(mask,                          Mask)
 #ifdef MOZ_ENABLE_MASK_AS_SHORTHAND
 COMPUTED_STYLE_PROP(mask_clip,                     MaskClip)
 COMPUTED_STYLE_PROP(mask_composite,                MaskComposite)
 COMPUTED_STYLE_PROP(mask_image,                    MaskImage)
 COMPUTED_STYLE_PROP(mask_mode,                     MaskMode)
 COMPUTED_STYLE_PROP(mask_origin,                   MaskOrigin)
 COMPUTED_STYLE_PROP(mask_position,                 MaskPosition)
+COMPUTED_STYLE_PROP(mask_position_x,               MaskPositionX)
+COMPUTED_STYLE_PROP(mask_position_y,               MaskPositionY)
 COMPUTED_STYLE_PROP(mask_repeat,                   MaskRepeat)
 COMPUTED_STYLE_PROP(mask_size,                     MaskSize)
 #endif
 COMPUTED_STYLE_PROP(mask_type,                     MaskType)
 COMPUTED_STYLE_PROP(paint_order,                   PaintOrder)
 COMPUTED_STYLE_PROP(shape_rendering,               ShapeRendering)
 COMPUTED_STYLE_PROP(stop_color,                    StopColor)
 COMPUTED_STYLE_PROP(stop_opacity,                  StopOpacity)